1. Field of the Invention
The present invention relates to a recording apparatus which performs a recording operation in accordance with inputted information.
2. Related Background Art
Among a plurality of printers, a laser beam printer is known as a recording apparatus which records an image by scanning a laser beam onto a rotary drum with a rotary polygon mirror and the like to form a latent image, and by transferring a developed latent image onto a recording sheet.
FIG. 5 shows the outline of the structure of a conventional laser beam printer which will be described while referring to FIG. 5.
In FIG. 5, reference numeral 1 represents a paper sheet as recording medium. A paper cassette 2 holds paper sheets 1. A paper feed cam 3 separates a single sheet from the top of the recording sheets 1 and conveys the tip portion of the separated sheet 1 to the position of paper feed rollers 4 and 4'. The paper feed cam 3 is driven by drive means (not shown) and intermittently rotated each time when a paper sheet is fed.
A reflective type photosensor 18 detects if a sheet is not present or not by detecting a reflected light from a sheet 1 via a aperture 19 formed in the bottom of the paper cassette 2.
When the sheet 1 reaches the clearance between the paper feed rollers 4 and 4' while being transported by means of the paper feed cam 3, the paper feed rollers 4 and 4' rotate while lightly squeezing the sheet 1 and further transport it.
When the tip end of the sheet 1 reaches the position of a registration shutter 5, the sheet 1 is stopped by the registration shutter 5. Whereas the paper feed rollers 4 and 4' continue to generate a transport torque and rotates while slip-contacting the sheet 1. In such condition, if a registration solenoid 6 is energized to move the registration shutter 5 upward in the figure, the transport stop of the sheet 1 is released so that the sheet 1 is sent to transport rollers 7 and 7'.
The registration shutter 5 is driven in synchro with the exposure timings of a laser beam 20. A photosensor 21 is disposed near the registration shutter 5 for detecting whether or not the sheet 1 is present at the registration shutter 5.
A rotary polygon mirror 52 driven by a polygon mirror motor 53 reflects the laser beam 20 and scans it. The laser beam 20 emitted from a semiconductor laser 51 is directed to a photosensitive drum 11 via the polygon mirror 52 and a reflective mirror 54 to thus form a latent image on the photosensitive drum 11. The beam 20 applied to the photosensitive drum 11 is detected by a beam detector 55 disposed at the scan start position of the beam 20 so that a BD signal is outputted which represents an image write timing in the main scan direction (horizontal synchro timing).
Thereafter, the sheet 1 is sent to the photosensitive drum 11 by means of the transport rollers 7 and 7' instead of the paper feed rollers 4 and 4'. A latent image exposed on the photosensitive drum 11 is developed by means of a combination of a cleaner 12, charger 13, developing unit 14, and transfer charger 15. The developed image is then transferred onto the sheet 1 which is fixed with fixing rollers 8 and 8' and ejected out to a stacker 10 by means of paper discharge rollers 9 and 9'. A symbol A show in FIG. 5 represents a guide for restricting the transport direction of the sheet 1.
A paper feed plate 16 allows paper sheets to be manually fed one after another to the printer, in addition to automatic paper feed from the paper cassette 2. A sheet manually fed by an operator at the position between the paper feed plate 16 and a manual feed roller 17 is transported while lightly pressed by the manual feed roller 17. In the similar manner as of the paper feed rollers 4 and 4', when the tip end of the sheet reaches the registration shutter 5, the paper feed roller 17 rotates while slip-contacting the sheet. The succeeding transport sequence is quite the same as the paper cassette feed.
The fixing roller 8 includes therein a fixing heater 24 which heats the roller surface thereof. A thermistor 23 for detection of the surface temperature of the fixing roller is disposed so as to slip-contact the surface of the fixing roller 8. The surface temperature of the fixing roller 8 is controlled to a predetermined temperature in accordance with the detected temperature by the thermistor 23, to thereby thermally fix an image recorded on the sheet 1.
A photosensor 22 is disposed at a position where it is detected if a sheet is present at the fixing rollers 8 and 8'.
The laser printer of such structure is not generally used independently, but is connected to external apparatus such as an image processing apparatus via interface cables (as a prior art of external apparatus, there are known for example U.S. Pat. No. 4,686,525, and U.S. Ser. No. 914,199 filed on Oct. 1, 1986 and others). Upon reception of a print command and image signal from the external apparatus via interface cables, the laser beam printer executes a predetermined print sequence (operation procedure) to print the image signal.
Signals for transmission between an external apparatus and a usual printer such as a laser printer are generally transferred in the form of serial signals at clock timings of a predetermined period. Therefore, an image clock signal generator for generating a signal transfer clock is provided either at the external apparatus or at the printer.
FIG. 6 shows an example of the structure of an external apparatus having an image clock signal generator.
Referring to FIG. 6, an external apparatus 217 outputs information regarding an image signal, control signal and the like to a printer 218. A signal line 62 is used for transfer of various control signals such as a print command and the like in the form of serial signals. A signal line 63 is used for transfer of an image signal VDO. A signal line 215 is used for transfer of a horizontal synchro signal BD. A main controller 65 for controlling the entirety of the printer is provided within the printer 218. Also provided for the printer is an interface circuit (not shown) for use in controlling input/output of the above-described signals.
The main controller controls the operations of the elements shown in FIG. 5, and supplies an image signal to a laser driver 66 which drives the semiconductor laser 51 (refer to FIG. 5).
The external apparatus 217 is provided with an image clock signal generator 61 for transmission of an image clock signal CLK to an image signal generator 60 which generates an image signal to be printed. With the constructed as above, when a horizontal synchro signal BD representative of the record start timing of one horizontal line is transmitted from the main controller to the image clock signal generator 61, the image clock signal generator 61 is triggered with this BD signal and generates a clock signal CLK (image clock signal) of a predetermined period. The image signal generator 60 transmits an image signal VDO to be printed to the main controller 65 via the signal line 63 in synchro with the image clock signal CLK. The main controller 65 converts the received image signal 63 into a laser drive signal 74 and sends it to the laser driver 66. If for example an image signal at a certain print position takes a bit "1", the laser drive signal is turned on to energize the semiconductor laser 51.
The laser beam is turned on and off in accordance with the laser drive signal to thus form a latent image on the photosensitive drum 11. The latent image is developed by adding toner thereto by means of the developing unit 14 and thereafter, transferred onto a paper sheet by means of the transfer charger 15 and fixed by the fixing rollers 8 and 8'. The recorded paper sheet is then ejected out.
FIG. 7 shows another example of the image clock signal generator.
In FIG. 7, elements having similar functions to those shown in FIG. 6 are designated by using identical reference numerals. The example shown in FIG. 7 has an image clock generator 61 on the side of a printer 218.
In conventional apparatus, there are a printer of the type which receives an image signal in synchro with an image clock signal generated by the external apparatus 217, and a printer of the type which receives an image signal in synchro with an image clock signal generated by the printer. There arises therefore a problem that the type of a printer should be selected in accordance with the type of an external apparatus. For instance, if both the external apparatus 217 and printer 218 are not provided with the image clock signal generator 61, then there is no compatibility between the external apparatus 217 and printer 218 which are not connectable accordingly.
It can be also considered that a specific image clock signal generator 61 may be provided at signal lines between an external apparatus 217 and a printer 218. However, this arrangement results in very complicated interconnections. In FIG. 8, elements having similar functions to those shown in FIG. 6 are represented by using identical reference numerals.
The assignee of the present application has proposed an improvement on recording apparatus as disclosed in U.S. Ser. No. 041,635 filed on Apr. 23, 1987, now abandoned and refiled as an FWC U.S. Ser. No. 07/291,349 filed on Dec. 29, 1988, now also abandoned and refiled as an FWC U.S. Ser. No. 07/554,187 filed July 20, 1990 and U.S. Pat. No. 4,695,849. A further improvement has been desired heretofore.